/*!
 * reveal.js
 * http://lab.hakim.se/reveal-js
 * MIT licensed
 *
 * Copyright (C) 2013 Hakim El Hattab, http://hakim.se
 */
var Reveal = (function () {

    'use strict';

    var SLIDES_SELECTOR = '.reveal .slides section',
        HORIZONTAL_SLIDES_SELECTOR = '.reveal .slides>section',
        VERTICAL_SLIDES_SELECTOR = '.reveal .slides>section.present>section',
        HOME_SLIDE_SELECTOR = '.reveal .slides>section:first-child',

    // Configurations defaults, can be overridden at initialization time
        config = {

            // The "normal" size of the presentation, aspect ratio will be preserved
            // when the presentation is scaled to fit different resolutions
            width: 960,
            height: 700,

            // Factor of the display size that should remain empty around the content
            margin: 0.1,

            // Bounds for smallest/largest possible scale to apply to content
            minScale: 0.2,
            maxScale: 1.0,

            // Display controls in the bottom right corner
            controls: true,

            // Display a presentation progress bar
            progress: true,

            // Push each slide change to the browser history
            history: false,

            // Enable keyboard shortcuts for navigation
            keyboard: true,

            // Enable the slide overview mode
            overview: true,

            // Vertical centring of slides
            center: true,

            // Enables touch navigation on devices with touch input
            touch: true,

            // Loop the presentation
            loop: false,

            // Change the presentation direction to be RTL
            rtl: false,

            // Turns fragments on and off globally
            fragments: true,

            // Number of milliseconds between automatically proceeding to the
            // next slide, disabled when set to 0, this value can be overwritten
            // by using a data-autoslide attribute on your slides
            autoSlide: 0,

            // Enable slide navigation via mouse wheel
            mouseWheel: false,

            // Apply a 3D roll to links on hover
            rollingLinks: true,

            // Opens links in an iframe preview overlay
            previewLinks: false,

            // Theme (see /css/theme)
            theme: null,

            // Transition style
            transition: 'default', // default/cube/page/concave/zoom/linear/fade/none

            // Transition speed
            transitionSpeed: 'default', // default/fast/slow

            // Transition style for full page slide backgrounds
            backgroundTransition: 'default', // default/linear

            // Script dependencies to load
            dependencies: []
        },

    // The current auto-slide duration
        autoSlide = 0,

    // The horizontal and vertical index of the currently active slide
        indexh = 0,
        indexv = 0,

    // The previous and current slide HTML elements
        previousSlide,
        currentSlide,

    // Slides may hold a data-state attribute which we pick up and apply
    // as a class to the body. This list contains the combined state of
    // all current slides.
        state = [],

    // The current scale of the presentation (see width/height config)
        scale = 1,

    // Cached references to DOM elements
        dom = {},

    // Detect support for CSS 3D transforms
        supports3DTransforms = 'WebkitPerspective' in document.body.style ||
            'MozPerspective' in document.body.style ||
            'msPerspective' in document.body.style ||
            'OPerspective' in document.body.style ||
            'perspective' in document.body.style,

    // Detect support for CSS 2D transforms
        supports2DTransforms = 'WebkitTransform' in document.body.style ||
            'MozTransform' in document.body.style ||
            'msTransform' in document.body.style ||
            'OTransform' in document.body.style ||
            'transform' in document.body.style,

    // Throttles mouse wheel navigation
        lastMouseWheelStep = 0,

    // An interval used to automatically move on to the next slide
        autoSlideTimeout = 0,

    // Delays updates to the URL due to a Chrome thumbnailer bug
        writeURLTimeout = 0,

    // A delay used to activate the overview mode
        activateOverviewTimeout = 0,

    // A delay used to deactivate the overview mode
        deactivateOverviewTimeout = 0,

    // Flags if the interaction event listeners are bound
        eventsAreBound = false,

    // Holds information about the currently ongoing touch input
        touch = {
            startX: 0,
            startY: 0,
            startSpan: 0,
            startCount: 0,
            handled: false,
            threshold: 80
        };

    /**
     * Starts up the presentation if the client is capable.
     */
    function initialize(options) {

        if (!supports2DTransforms && !supports3DTransforms) {
            document.body.setAttribute('class', 'no-transforms');

            // If the browser doesn't support core features we won't be
            // using JavaScript to control the presentation
            return;
        }

        // Force a layout when the whole page, incl fonts, has loaded
        window.addEventListener('load', layout, false);

        // Copy options over to our config object
        extend(config, options);

        // Hide the address bar in mobile browsers
        hideAddressBar();

        // Loads the dependencies and continues to #start() once done
        load();

    }

    /**
     * Finds and stores references to DOM elements which are
     * required by the presentation. If a required element is
     * not found, it is created.
     */
    function setupDOM() {

        // Cache references to key DOM elements
        dom.theme = document.querySelector('#theme');
        dom.wrapper = document.querySelector('.reveal');
        dom.slides = document.querySelector('.reveal .slides');

        // Background element
        if (!document.querySelector('.reveal .backgrounds')) {
            dom.background = document.createElement('div');
            dom.background.classList.add('backgrounds');
            dom.wrapper.appendChild(dom.background);
        }

        // Progress bar
        if (!dom.wrapper.querySelector('.progress')) {
            var progressElement = document.createElement('div');
            progressElement.classList.add('progress');
            progressElement.innerHTML = '<span></span>';
            dom.wrapper.appendChild(progressElement);
        }

        // Arrow controls
        if (!dom.wrapper.querySelector('.controls')) {
            var controlsElement = document.createElement('aside');
            controlsElement.classList.add('controls');
            controlsElement.innerHTML = '<div class="navigate-left"></div>' +
                '<div class="navigate-right"></div>' +
                '<div class="navigate-up"></div>' +
                '<div class="navigate-down"></div>';
            dom.wrapper.appendChild(controlsElement);
        }

        // State background element [DEPRECATED]
        if (!dom.wrapper.querySelector('.state-background')) {
            var stateBackgroundElement = document.createElement('div');
            stateBackgroundElement.classList.add('state-background');
            dom.wrapper.appendChild(stateBackgroundElement);
        }

        // Overlay graphic which is displayed during the paused mode
        if (!dom.wrapper.querySelector('.pause-overlay')) {
            var pausedElement = document.createElement('div');
            pausedElement.classList.add('pause-overlay');
            dom.wrapper.appendChild(pausedElement);
        }

        // Cache references to elements
        dom.progress = document.querySelector('.reveal .progress');
        dom.progressbar = document.querySelector('.reveal .progress span');

        if (config.controls) {
            dom.controls = document.querySelector('.reveal .controls');

            // There can be multiple instances of controls throughout the page
            dom.controlsLeft = toArray(document.querySelectorAll('.navigate-left'));
            dom.controlsRight = toArray(document.querySelectorAll('.navigate-right'));
            dom.controlsUp = toArray(document.querySelectorAll('.navigate-up'));
            dom.controlsDown = toArray(document.querySelectorAll('.navigate-down'));
            dom.controlsPrev = toArray(document.querySelectorAll('.navigate-prev'));
            dom.controlsNext = toArray(document.querySelectorAll('.navigate-next'));
        }

    }

    /**
     * Creates the slide background elements and appends them
     * to the background container. One element is created per
     * slide no matter if the given slide has visible background.
     */
    function createBackgrounds() {

        if (isPrintingPDF()) {
            document.body.classList.add('print-pdf');
        }

        // Clear prior backgrounds
        dom.background.innerHTML = '';
        dom.background.classList.add('no-transition');

        // Helper method for creating a background element for the
        // given slide
        function _createBackground(slide, container) {

            var data = {
                background: slide.getAttribute('data-background'),
                backgroundSize: slide.getAttribute('data-background-size'),
                backgroundColor: slide.getAttribute('data-background-color'),
                backgroundRepeat: slide.getAttribute('data-background-repeat'),
                backgroundPosition: slide.getAttribute('data-background-position'),
                backgroundTransition: slide.getAttribute('data-background-transition')
            };

            var element = document.createElement('div');
            element.className = 'slide-background';

            if (data.background) {
                // Auto-wrap image urls in url(...)
                if (/^(http|file|\/\/)/gi.test(data.background)) {
                    element.style.backgroundImage = 'url(' + data.background + ')';
                }
                else {
                    element.style.background = data.background;
                }
            }

            // Additional and optional background properties
            if (data.backgroundSize) element.style.backgroundSize = data.backgroundSize;
            if (data.backgroundColor) element.style.backgroundColor = data.backgroundColor;
            if (data.backgroundRepeat) element.style.backgroundRepeat = data.backgroundRepeat;
            if (data.backgroundPosition) element.style.backgroundPosition = data.backgroundPosition;
            if (data.backgroundTransition) element.setAttribute('data-background-transition', data.backgroundTransition);

            container.appendChild(element);

            return element;

        }

        // Iterate over all horizontal slides
        toArray(document.querySelectorAll(HORIZONTAL_SLIDES_SELECTOR)).forEach(function (slideh) {

            var backgroundStack;

            if (isPrintingPDF()) {
                backgroundStack = _createBackground(slideh, slideh);
            }
            else {
                backgroundStack = _createBackground(slideh, dom.background);
            }

            // Iterate over all vertical slides
            toArray(slideh.querySelectorAll('section')).forEach(function (slidev) {

                if (isPrintingPDF()) {
                    _createBackground(slidev, slidev);
                }
                else {
                    _createBackground(slidev, backgroundStack);
                }

            });

        });

    }

    /**
     * Hides the address bar if we're on a mobile device.
     */
    function hideAddressBar() {

        if (/iphone|ipod|android/gi.test(navigator.userAgent) && !/crios/gi.test(navigator.userAgent)) {
            // Events that should trigger the address bar to hide
            window.addEventListener('load', removeAddressBar, false);
            window.addEventListener('orientationchange', removeAddressBar, false);
        }

    }

    /**
     * Loads the dependencies of reveal.js. Dependencies are
     * defined via the configuration option 'dependencies'
     * and will be loaded prior to starting/binding reveal.js.
     * Some dependencies may have an 'async' flag, if so they
     * will load after reveal.js has been started up.
     */
    function load() {

        var scripts = [],
            scriptsAsync = [];

        for (var i = 0, len = config.dependencies.length; i < len; i++) {
            var s = config.dependencies[i];

            // Load if there's no condition or the condition is truthy
            if (!s.condition || s.condition()) {
                if (s.async) {
                    scriptsAsync.push(s.src);
                }
                else {
                    scripts.push(s.src);
                }

                // Extension may contain callback functions
                if (typeof s.callback === 'function') {
                    head.ready(s.src.match(/([\w\d_\-]*)\.?js$|[^\\\/]*$/i)[0], s.callback);
                }
            }
        }

        // Called once synchronous scripts finish loading
        function proceed() {
            if (scriptsAsync.length) {
                // Load asynchronous scripts
                head.js.apply(null, scriptsAsync);
            }

            start();
        }

        if (scripts.length) {
            head.ready(proceed);

            // Load synchronous scripts
            head.js.apply(null, scripts);
        }
        else {
            proceed();
        }

    }

    /**
     * Starts up reveal.js by binding input events and navigating
     * to the current URL deeplink if there is one.
     */
    function start() {

        // Make sure we've got all the DOM elements we need
        setupDOM();

        // Updates the presentation to match the current configuration values
        configure();

        // Read the initial hash
        readURL();

        // Notify listeners that the presentation is ready but use a 1ms
        // timeout to ensure it's not fired synchronously after #initialize()
        setTimeout(function () {
            dispatchEvent('ready', {
                'indexh': indexh,
                'indexv': indexv,
                'currentSlide': currentSlide
            });
        }, 1);

    }

    /**
     * Applies the configuration settings from the config
     * object. May be called multiple times.
     */
    function configure(options) {

        dom.wrapper.classList.remove(config.transition);

        // New config options may be passed when this method
        // is invoked through the API after initialization
        if (typeof options === 'object') extend(config, options);

        // Force linear transition based on browser capabilities
        if (supports3DTransforms === false) config.transition = 'linear';

        dom.wrapper.classList.add(config.transition);

        dom.wrapper.setAttribute('data-transition-speed', config.transitionSpeed);
        dom.wrapper.setAttribute('data-background-transition', config.backgroundTransition);

        if (dom.controls) {
            dom.controls.style.display = ( config.controls && dom.controls ) ? 'block' : 'none';
        }

        if (dom.progress) {
            dom.progress.style.display = ( config.progress && dom.progress ) ? 'block' : 'none';
        }

        if (config.rtl) {
            dom.wrapper.classList.add('rtl');
        }
        else {
            dom.wrapper.classList.remove('rtl');
        }

        if (config.center) {
            dom.wrapper.classList.add('center');
        }
        else {
            dom.wrapper.classList.remove('center');
        }

        if (config.mouseWheel) {
            document.addEventListener('DOMMouseScroll', onDocumentMouseScroll, false); // FF
            document.addEventListener('mousewheel', onDocumentMouseScroll, false);
        }
        else {
            document.removeEventListener('DOMMouseScroll', onDocumentMouseScroll, false); // FF
            document.removeEventListener('mousewheel', onDocumentMouseScroll, false);
        }

        // Rolling 3D links
        if (config.rollingLinks) {
            enableRollingLinks();
        }
        else {
            disableRollingLinks();
        }

        // Iframe link previews
        if (config.previewLinks) {
            enablePreviewLinks();
        }
        else {
            disablePreviewLinks();
            enablePreviewLinks('[data-preview-link]');
        }

        // Load the theme in the config, if it's not already loaded
        if (config.theme && dom.theme) {
            var themeURL = dom.theme.getAttribute('href');
            var themeFinder = /[^\/]*?(?=\.css)/;
            var themeName = themeURL.match(themeFinder)[0];

            if (config.theme !== themeName) {
                themeURL = themeURL.replace(themeFinder, config.theme);
                dom.theme.setAttribute('href', themeURL);
            }
        }

        sync();

    }

    /**
     * Binds all event listeners.
     */
    function addEventListeners() {

        eventsAreBound = true;

        window.addEventListener('hashchange', onWindowHashChange, false);
        window.addEventListener('resize', onWindowResize, false);

        if (config.touch) {
            dom.wrapper.addEventListener('touchstart', onTouchStart, false);
            dom.wrapper.addEventListener('touchmove', onTouchMove, false);
            dom.wrapper.addEventListener('touchend', onTouchEnd, false);

            // Support pointer-style touch interaction as well
            if (window.navigator.msPointerEnabled) {
                dom.wrapper.addEventListener('MSPointerDown', onPointerDown, false);
                dom.wrapper.addEventListener('MSPointerMove', onPointerMove, false);
                dom.wrapper.addEventListener('MSPointerUp', onPointerUp, false);
            }
        }

        if (config.keyboard) {
            document.addEventListener('keydown', onDocumentKeyDown, false);
        }

        if (config.progress && dom.progress) {
            dom.progress.addEventListener('click', onProgressClicked, false);
        }

        if (config.controls && dom.controls) {
            ['touchstart', 'click'].forEach(function (eventName) {
                dom.controlsLeft.forEach(function (el) {
                    el.addEventListener(eventName, onNavigateLeftClicked, false);
                });
                dom.controlsRight.forEach(function (el) {
                    el.addEventListener(eventName, onNavigateRightClicked, false);
                });
                dom.controlsUp.forEach(function (el) {
                    el.addEventListener(eventName, onNavigateUpClicked, false);
                });
                dom.controlsDown.forEach(function (el) {
                    el.addEventListener(eventName, onNavigateDownClicked, false);
                });
                dom.controlsPrev.forEach(function (el) {
                    el.addEventListener(eventName, onNavigatePrevClicked, false);
                });
                dom.controlsNext.forEach(function (el) {
                    el.addEventListener(eventName, onNavigateNextClicked, false);
                });
            });
        }

    }

    /**
     * Unbinds all event listeners.
     */
    function removeEventListeners() {

        eventsAreBound = false;

        document.removeEventListener('keydown', onDocumentKeyDown, false);
        window.removeEventListener('hashchange', onWindowHashChange, false);
        window.removeEventListener('resize', onWindowResize, false);

        dom.wrapper.removeEventListener('touchstart', onTouchStart, false);
        dom.wrapper.removeEventListener('touchmove', onTouchMove, false);
        dom.wrapper.removeEventListener('touchend', onTouchEnd, false);

        if (window.navigator.msPointerEnabled) {
            dom.wrapper.removeEventListener('MSPointerDown', onPointerDown, false);
            dom.wrapper.removeEventListener('MSPointerMove', onPointerMove, false);
            dom.wrapper.removeEventListener('MSPointerUp', onPointerUp, false);
        }

        if (config.progress && dom.progress) {
            dom.progress.removeEventListener('click', onProgressClicked, false);
        }

        if (config.controls && dom.controls) {
            ['touchstart', 'click'].forEach(function (eventName) {
                dom.controlsLeft.forEach(function (el) {
                    el.removeEventListener(eventName, onNavigateLeftClicked, false);
                });
                dom.controlsRight.forEach(function (el) {
                    el.removeEventListener(eventName, onNavigateRightClicked, false);
                });
                dom.controlsUp.forEach(function (el) {
                    el.removeEventListener(eventName, onNavigateUpClicked, false);
                });
                dom.controlsDown.forEach(function (el) {
                    el.removeEventListener(eventName, onNavigateDownClicked, false);
                });
                dom.controlsPrev.forEach(function (el) {
                    el.removeEventListener(eventName, onNavigatePrevClicked, false);
                });
                dom.controlsNext.forEach(function (el) {
                    el.removeEventListener(eventName, onNavigateNextClicked, false);
                });
            });
        }

    }

    /**
     * Extend object a with the properties of object b.
     * If there's a conflict, object b takes precedence.
     */
    function extend(a, b) {

        for (var i in b) {
            a[i] = b[i];
        }

    }

    /**
     * Converts the target object to an array.
     */
    function toArray(o) {

        return Array.prototype.slice.call(o);

    }

    /**
     * Measures the distance in pixels between point a
     * and point b.
     *
     * @param {Object} a point with x/y properties
     * @param {Object} b point with x/y properties
     */
    function distanceBetween(a, b) {

        var dx = a.x - b.x,
            dy = a.y - b.y;

        return Math.sqrt(dx * dx + dy * dy);

    }

    /**
     * Retrieves the height of the given element by looking
     * at the position and height of its immediate children.
     */
    function getAbsoluteHeight(element) {

        var height = 0;

        if (element) {
            var absoluteChildren = 0;

            toArray(element.childNodes).forEach(function (child) {

                if (typeof child.offsetTop === 'number' && child.style) {
                    // Count # of abs children
                    if (child.style.position === 'absolute') {
                        absoluteChildren += 1;
                    }

                    height = Math.max(height, child.offsetTop + child.offsetHeight);
                }

            });

            // If there are no absolute children, use offsetHeight
            if (absoluteChildren === 0) {
                height = element.offsetHeight;
            }

        }

        return height;

    }

    /**
     * Checks if this instance is being used to print a PDF.
     */
    function isPrintingPDF() {

        return ( /print-pdf/gi ).test(window.location.search);

    }

    /**
     * Causes the address bar to hide on mobile devices,
     * more vertical space ftw.
     */
    function removeAddressBar() {

        if (window.orientation === 0) {
            document.documentElement.style.overflow = 'scroll';
            document.body.style.height = '120%';
        }
        else {
            document.documentElement.style.overflow = '';
            document.body.style.height = '100%';
        }

        setTimeout(function () {
            window.scrollTo(0, 1);
        }, 10);

    }

    /**
     * Dispatches an event of the specified type from the
     * reveal DOM element.
     */
    function dispatchEvent(type, properties) {

        var event = document.createEvent("HTMLEvents", 1, 2);
        event.initEvent(type, true, true);
        extend(event, properties);
        dom.wrapper.dispatchEvent(event);

    }

    /**
     * Wrap all links in 3D goodness.
     */
    function enableRollingLinks() {

        if (supports3DTransforms && !( 'msPerspective' in document.body.style )) {
            var anchors = document.querySelectorAll(SLIDES_SELECTOR + ' a:not(.image)');

            for (var i = 0, len = anchors.length; i < len; i++) {
                var anchor = anchors[i];

                if (anchor.textContent && !anchor.querySelector('*') && ( !anchor.className || !anchor.classList.contains(anchor, 'roll') )) {
                    var span = document.createElement('span');
                    span.setAttribute('data-title', anchor.text);
                    span.innerHTML = anchor.innerHTML;

                    anchor.classList.add('roll');
                    anchor.innerHTML = '';
                    anchor.appendChild(span);
                }
            }
        }

    }

    /**
     * Unwrap all 3D links.
     */
    function disableRollingLinks() {

        var anchors = document.querySelectorAll(SLIDES_SELECTOR + ' a.roll');

        for (var i = 0, len = anchors.length; i < len; i++) {
            var anchor = anchors[i];
            var span = anchor.querySelector('span');

            if (span) {
                anchor.classList.remove('roll');
                anchor.innerHTML = span.innerHTML;
            }
        }

    }

    /**
     * Bind preview frame links.
     */
    function enablePreviewLinks(selector) {

        var anchors = toArray(document.querySelectorAll(selector ? selector : 'a'));

        anchors.forEach(function (element) {
            if (/^(http|www)/gi.test(element.getAttribute('href'))) {
                element.addEventListener('click', onPreviewLinkClicked, false);
            }
        });

    }

    /**
     * Unbind preview frame links.
     */
    function disablePreviewLinks() {

        var anchors = toArray(document.querySelectorAll('a'));

        anchors.forEach(function (element) {
            if (/^(http|www)/gi.test(element.getAttribute('href'))) {
                element.removeEventListener('click', onPreviewLinkClicked, false);
            }
        });

    }

    /**
     * Opens a preview window for the target URL.
     */
    function openPreview(url) {

        closePreview();

        dom.preview = document.createElement('div');
        dom.preview.classList.add('preview-link-overlay');
        dom.wrapper.appendChild(dom.preview);

        dom.preview.innerHTML = [
            '<header>',
            '<a class="close" href="#"><span class="icon"></span></a>',
            '<a class="external" href="' + url + '" target="_blank"><span class="icon"></span></a>',
            '</header>',
            '<div class="spinner"></div>',
            '<div class="viewport">',
            '<iframe src="' + url + '"></iframe>',
            '</div>'
        ].join('');

        dom.preview.querySelector('iframe').addEventListener('load', function (event) {
            dom.preview.classList.add('loaded');
        }, false);

        dom.preview.querySelector('.close').addEventListener('click', function (event) {
            closePreview();
            event.preventDefault();
        }, false);

        dom.preview.querySelector('.external').addEventListener('click', function (event) {
            closePreview();
        }, false);

        setTimeout(function () {
            dom.preview.classList.add('visible');
        }, 1);

    }

    /**
     * Closes the iframe preview window.
     */
    function closePreview() {

        if (dom.preview) {
            dom.preview.setAttribute('src', '');
            dom.preview.parentNode.removeChild(dom.preview);
            dom.preview = null;
        }

    }

    /**
     * Return a sorted fragments list, ordered by an increasing
     * "data-fragment-index" attribute.
     *
     * Fragments will be revealed in the order that they are returned by
     * this function, so you can use the index attributes to control the
     * order of fragment appearance.
     *
     * To maintain a sensible default fragment order, fragments are presumed
     * to be passed in document order. This function adds a "fragment-index"
     * attribute to each node if such an attribute is not already present,
     * and sets that attribute to an integer value which is the position of
     * the fragment within the fragments list.
     */
    function sortFragments(fragments) {

        var a = toArray(fragments);

        a.forEach(function (el, idx) {
            if (!el.hasAttribute('data-fragment-index')) {
                el.setAttribute('data-fragment-index', idx);
            }
        });

        a.sort(function (l, r) {
            return l.getAttribute('data-fragment-index') - r.getAttribute('data-fragment-index');
        });

        return a;

    }

    /**
     * Applies JavaScript-controlled layout rules to the
     * presentation.
     */
    function layout() {

        if (dom.wrapper && !isPrintingPDF()) {

            // Available space to scale within
            var availableWidth = dom.wrapper.offsetWidth,
                availableHeight = dom.wrapper.offsetHeight;

            // Reduce available space by margin
            availableWidth -= ( availableHeight * config.margin );
            availableHeight -= ( availableHeight * config.margin );

            // Dimensions of the content
            var slideWidth = config.width,
                slideHeight = config.height;

            // Slide width may be a percentage of available width
            if (typeof slideWidth === 'string' && /%$/.test(slideWidth)) {
                slideWidth = parseInt(slideWidth, 10) / 100 * availableWidth;
            }

            // Slide height may be a percentage of available height
            if (typeof slideHeight === 'string' && /%$/.test(slideHeight)) {
                slideHeight = parseInt(slideHeight, 10) / 100 * availableHeight;
            }

            dom.slides.style.width = slideWidth + 'px';
            dom.slides.style.height = slideHeight + 'px';

            // Determine scale of content to fit within available space
            scale = Math.min(availableWidth / slideWidth, availableHeight / slideHeight);

            // Respect max/min scale settings
            scale = Math.max(scale, config.minScale);
            scale = Math.min(scale, config.maxScale);

            // Prefer applying scale via zoom since Chrome blurs scaled content
            // with nested transforms
            if (typeof dom.slides.style.zoom !== 'undefined' && !navigator.userAgent.match(/(iphone|ipod|ipad|android)/gi)) {
                dom.slides.style.zoom = scale;
            }
            // Apply scale transform as a fallback
            else {
                var transform = 'translate(-50%, -50%) scale(' + scale + ') translate(50%, 50%)';

                dom.slides.style.WebkitTransform = transform;
                dom.slides.style.MozTransform = transform;
                dom.slides.style.msTransform = transform;
                dom.slides.style.OTransform = transform;
                dom.slides.style.transform = transform;
            }

            // Select all slides, vertical and horizontal
            var slides = toArray(document.querySelectorAll(SLIDES_SELECTOR));

            for (var i = 0, len = slides.length; i < len; i++) {
                var slide = slides[i];

                // Don't bother updating invisible slides
                if (slide.style.display === 'none') {
                    continue;
                }

                if (config.center) {
                    // Vertical stacks are not centred since their section
                    // children will be
                    if (slide.classList.contains('stack')) {
                        slide.style.top = 0;
                    }
                    else {
                        slide.style.top = Math.max(-( getAbsoluteHeight(slide) / 2 ) - 20, -slideHeight / 2) + 'px';
                    }
                }
                else {
                    slide.style.top = '';
                }

            }

            updateProgress();

        }

    }

    /**
     * Stores the vertical index of a stack so that the same
     * vertical slide can be selected when navigating to and
     * from the stack.
     *
     * @param {HTMLElement} stack The vertical stack element
     * @param {int} v Index to memorize
     */
    function setPreviousVerticalIndex(stack, v) {

        if (typeof stack === 'object' && typeof stack.setAttribute === 'function') {
            stack.setAttribute('data-previous-indexv', v || 0);
        }

    }

    /**
     * Retrieves the vertical index which was stored using
     * #setPreviousVerticalIndex() or 0 if no previous index
     * exists.
     *
     * @param {HTMLElement} stack The vertical stack element
     */
    function getPreviousVerticalIndex(stack) {

        if (typeof stack === 'object' && typeof stack.setAttribute === 'function' && stack.classList.contains('stack')) {
            // Prefer manually defined start-indexv
            var attributeName = stack.hasAttribute('data-start-indexv') ? 'data-start-indexv' : 'data-previous-indexv';

            return parseInt(stack.getAttribute(attributeName) || 0, 10);
        }

        return 0;

    }

    /**
     * Displays the overview of slides (quick nav) by
     * scaling down and arranging all slide elements.
     *
     * Experimental feature, might be dropped if perf
     * can't be improved.
     */
    function activateOverview() {

        // Only proceed if enabled in config
        if (config.overview) {

            // Don't auto-slide while in overview mode
            cancelAutoSlide();

            var wasActive = dom.wrapper.classList.contains('overview');

            dom.wrapper.classList.add('overview');
            dom.wrapper.classList.remove('exit-overview');

            clearTimeout(activateOverviewTimeout);
            clearTimeout(deactivateOverviewTimeout);

            // Not the pretties solution, but need to let the overview
            // class apply first so that slides are measured accurately
            // before we can position them
            activateOverviewTimeout = setTimeout(function () {

                var horizontalSlides = document.querySelectorAll(HORIZONTAL_SLIDES_SELECTOR);

                for (var i = 0, len1 = horizontalSlides.length; i < len1; i++) {
                    var hslide = horizontalSlides[i],
                        hoffset = config.rtl ? -105 : 105,
                        htransform = 'translateZ(-2500px) translate(' + ( ( i - indexh ) * hoffset ) + '%, 0%)';

                    hslide.setAttribute('data-index-h', i);
                    hslide.style.display = 'block';
                    hslide.style.WebkitTransform = htransform;
                    hslide.style.MozTransform = htransform;
                    hslide.style.msTransform = htransform;
                    hslide.style.OTransform = htransform;
                    hslide.style.transform = htransform;

                    if (hslide.classList.contains('stack')) {

                        var verticalSlides = hslide.querySelectorAll('section');

                        for (var j = 0, len2 = verticalSlides.length; j < len2; j++) {
                            var verticalIndex = i === indexh ? indexv : getPreviousVerticalIndex(hslide);

                            var vslide = verticalSlides[j],
                                vtransform = 'translate(0%, ' + ( ( j - verticalIndex ) * 105 ) + '%)';

                            vslide.setAttribute('data-index-h', i);
                            vslide.setAttribute('data-index-v', j);
                            vslide.style.display = 'block';
                            vslide.style.WebkitTransform = vtransform;
                            vslide.style.MozTransform = vtransform;
                            vslide.style.msTransform = vtransform;
                            vslide.style.OTransform = vtransform;
                            vslide.style.transform = vtransform;

                            // Navigate to this slide on click
                            vslide.addEventListener('click', onOverviewSlideClicked, true);
                        }

                    }
                    else {

                        // Navigate to this slide on click
                        hslide.addEventListener('click', onOverviewSlideClicked, true);

                    }
                }

                layout();

                if (!wasActive) {
                    // Notify observers of the overview showing
                    dispatchEvent('overviewshown', {
                        'indexh': indexh,
                        'indexv': indexv,
                        'currentSlide': currentSlide
                    });
                }

            }, 10);

        }

    }

    /**
     * Exits the slide overview and enters the currently
     * active slide.
     */
    function deactivateOverview() {

        // Only proceed if enabled in config
        if (config.overview) {

            clearTimeout(activateOverviewTimeout);
            clearTimeout(deactivateOverviewTimeout);

            dom.wrapper.classList.remove('overview');

            // Temporarily add a class so that transitions can do different things
            // depending on whether they are exiting/entering overview, or just
            // moving from slide to slide
            dom.wrapper.classList.add('exit-overview');

            deactivateOverviewTimeout = setTimeout(function () {
                dom.wrapper.classList.remove('exit-overview');
            }, 10);

            // Select all slides
            var slides = toArray(document.querySelectorAll(SLIDES_SELECTOR));

            for (var i = 0, len = slides.length; i < len; i++) {
                var element = slides[i];

                element.style.display = '';

                // Resets all transforms to use the external styles
                element.style.WebkitTransform = '';
                element.style.MozTransform = '';
                element.style.msTransform = '';
                element.style.OTransform = '';
                element.style.transform = '';

                element.removeEventListener('click', onOverviewSlideClicked, true);
            }

            slide(indexh, indexv);

            cueAutoSlide();

            // Notify observers of the overview hiding
            dispatchEvent('overviewhidden', {
                'indexh': indexh,
                'indexv': indexv,
                'currentSlide': currentSlide
            });

        }
    }

    /**
     * Toggles the slide overview mode on and off.
     *
     * @param {Boolean} override Optional flag which overrides the
     * toggle logic and forcibly sets the desired state. True means
     * overview is open, false means it's closed.
     */
    function toggleOverview(override) {

        if (typeof override === 'boolean') {
            override ? activateOverview() : deactivateOverview();
        }
        else {
            isOverview() ? deactivateOverview() : activateOverview();
        }

    }

    /**
     * Checks if the overview is currently active.
     *
     * @return {Boolean} true if the overview is active,
     * false otherwise
     */
    function isOverview() {

        return dom.wrapper.classList.contains('overview');

    }

    /**
     * Checks if the current or specified slide is vertical
     * (nested within another slide).
     *
     * @param {HTMLElement} slide [optional] The slide to check
     * orientation of
     */
    function isVerticalSlide(slide) {

        // Prefer slide argument, otherwise use current slide
        slide = slide ? slide : currentSlide;

        return slide && !!slide.parentNode.nodeName.match(/section/i);

    }

    /**
     * Handling the fullscreen functionality via the fullscreen API
     *
     * @see http://fullscreen.spec.whatwg.org/
     * @see https://developer.mozilla.org/en-US/docs/DOM/Using_fullscreen_mode
     */
    function enterFullscreen() {

        var element = document.body;

        // Check which implementation is available
        var requestMethod = element.requestFullScreen ||
            element.webkitRequestFullscreen ||
            element.webkitRequestFullScreen ||
            element.mozRequestFullScreen ||
            element.msRequestFullScreen;

        if (requestMethod) {
            requestMethod.apply(element);
        }

    }

    /**
     * Enters the paused mode which fades everything on screen to
     * black.
     */
    function pause() {

        var wasPaused = dom.wrapper.classList.contains('paused');

        cancelAutoSlide();
        dom.wrapper.classList.add('paused');

        if (wasPaused === false) {
            dispatchEvent('paused');
        }

    }

    /**
     * Exits from the paused mode.
     */
    function resume() {

        var wasPaused = dom.wrapper.classList.contains('paused');
        dom.wrapper.classList.remove('paused');

        cueAutoSlide();

        if (wasPaused) {
            dispatchEvent('resumed');
        }

    }

    /**
     * Toggles the paused mode on and off.
     */
    function togglePause() {

        if (isPaused()) {
            resume();
        }
        else {
            pause();
        }

    }

    /**
     * Checks if we are currently in the paused mode.
     */
    function isPaused() {

        return dom.wrapper.classList.contains('paused');

    }

    /**
     * Steps from the current point in the presentation to the
     * slide which matches the specified horizontal and vertical
     * indices.
     *
     * @param {int} h Horizontal index of the target slide
     * @param {int} v Vertical index of the target slide
     * @param {int} f Optional index of a fragment within the
     * target slide to activate
     * @param {int} o Optional origin for use in multimaster environments
     */
    function slide(h, v, f, o) {

        // Remember where we were at before
        previousSlide = currentSlide;

        // Query all horizontal slides in the deck
        var horizontalSlides = document.querySelectorAll(HORIZONTAL_SLIDES_SELECTOR);

        // If no vertical index is specified and the upcoming slide is a
        // stack, resume at its previous vertical index
        if (v === undefined) {
            v = getPreviousVerticalIndex(horizontalSlides[h]);
        }

        // If we were on a vertical stack, remember what vertical index
        // it was on so we can resume at the same position when returning
        if (previousSlide && previousSlide.parentNode && previousSlide.parentNode.classList.contains('stack')) {
            setPreviousVerticalIndex(previousSlide.parentNode, indexv);
        }

        // Remember the state before this slide
        var stateBefore = state.concat();

        // Reset the state array
        state.length = 0;

        var indexhBefore = indexh,
            indexvBefore = indexv;

        // Activate and transition to the new slide
        indexh = updateSlides(HORIZONTAL_SLIDES_SELECTOR, h === undefined ? indexh : h);
        indexv = updateSlides(VERTICAL_SLIDES_SELECTOR, v === undefined ? indexv : v);

        layout();

        // Apply the new state
        stateLoop: for (var i = 0, len = state.length; i < len; i++) {
            // Check if this state existed on the previous slide. If it
            // did, we will avoid adding it repeatedly
            for (var j = 0; j < stateBefore.length; j++) {
                if (stateBefore[j] === state[i]) {
                    stateBefore.splice(j, 1);
                    continue stateLoop;
                }
            }

            document.documentElement.classList.add(state[i]);

            // Dispatch custom event matching the state's name
            dispatchEvent(state[i]);
        }

        // Clean up the remains of the previous state
        while (stateBefore.length) {
            document.documentElement.classList.remove(stateBefore.pop());
        }

        // If the overview is active, re-activate it to update positions
        if (isOverview()) {
            activateOverview();
        }

        // Update the URL hash after a delay since updating it mid-transition
        // is likely to cause visual lag
        writeURL(1500);

        // Find the current horizontal slide and any possible vertical slides
        // within it
        var currentHorizontalSlide = horizontalSlides[indexh],
            currentVerticalSlides = currentHorizontalSlide.querySelectorAll('section');

        // Store references to the previous and current slides
        currentSlide = currentVerticalSlides[indexv] || currentHorizontalSlide;


        // Show fragment, if specified
        if (typeof f !== 'undefined') {
            var fragments = sortFragments(currentSlide.querySelectorAll('.fragment'));

            toArray(fragments).forEach(function (fragment, indexf) {
                if (indexf < f) {
                    fragment.classList.add('visible');
                }
                else {
                    fragment.classList.remove('visible');
                }
            });
        }

        // Dispatch an event if the slide changed
        var slideChanged = ( indexh !== indexhBefore || indexv !== indexvBefore );
        if (slideChanged) {
            dispatchEvent('slidechanged', {
                'indexh': indexh,
                'indexv': indexv,
                'previousSlide': previousSlide,
                'currentSlide': currentSlide,
                'origin': o
            });
        }
        else {
            // Ensure that the previous slide is never the same as the current
            previousSlide = null;
        }

        // Solves an edge case where the previous slide maintains the
        // 'present' class when navigating between adjacent vertical
        // stacks
        if (previousSlide) {
            previousSlide.classList.remove('present');

            // Reset all slides upon navigate to home
            // Issue: #285
            if (document.querySelector(HOME_SLIDE_SELECTOR).classList.contains('present')) {
                // Launch async task
                setTimeout(function () {
                    var slides = toArray(document.querySelectorAll(HORIZONTAL_SLIDES_SELECTOR + '.stack')), i;
                    for (i in slides) {
                        if (slides[i]) {
                            // Reset stack
                            setPreviousVerticalIndex(slides[i], 0);
                        }
                    }
                }, 0);
            }
        }

        // Handle embedded content
        if (slideChanged) {
            stopEmbeddedContent(previousSlide);
            startEmbeddedContent(currentSlide);
        }

        updateControls();
        updateProgress();
        updateBackground();

    }

    /**
     * Syncs the presentation with the current DOM. Useful
     * when new slides or control elements are added or when
     * the configuration has changed.
     */
    function sync() {

        // Subscribe to input
        removeEventListeners();
        addEventListeners();

        // Force a layout to make sure the current config is accounted for
        layout();

        // Reflect the current autoSlide value
        autoSlide = config.autoSlide;

        // Start auto-sliding if it's enabled
        cueAutoSlide();

        // Re-create the slide backgrounds
        createBackgrounds();

        updateControls();
        updateProgress();
        updateBackground();

    }

    /**
     * Updates one dimension of slides by showing the slide
     * with the specified index.
     *
     * @param {String} selector A CSS selector that will fetch
     * the group of slides we are working with
     * @param {Number} index The index of the slide that should be
     * shown
     *
     * @return {Number} The index of the slide that is now shown,
     * might differ from the passed in index if it was out of
     * bounds.
     */
    function updateSlides(selector, index) {

        // Select all slides and convert the NodeList result to
        // an array
        var slides = toArray(document.querySelectorAll(selector)),
            slidesLength = slides.length;

        if (slidesLength) {

            // Should the index loop?
            if (config.loop) {
                index %= slidesLength;

                if (index < 0) {
                    index = slidesLength + index;
                }
            }

            // Enforce max and minimum index bounds
            index = Math.max(Math.min(index, slidesLength - 1), 0);

            for (var i = 0; i < slidesLength; i++) {
                var element = slides[i];

                // Optimization; hide all slides that are three or more steps
                // away from the present slide
                if (isOverview() === false) {
                    // The distance loops so that it measures 1 between the first
                    // and last slides
                    var distance = Math.abs(( index - i ) % ( slidesLength - 3 )) || 0;

                    element.style.display = distance > 3 ? 'none' : 'block';
                }

                var reverse = config.rtl && !isVerticalSlide(element);

                element.classList.remove('past');
                element.classList.remove('present');
                element.classList.remove('future');

                // http://www.w3.org/html/wg/drafts/html/master/editing.html#the-hidden-attribute
                element.setAttribute('hidden', '');

                if (i < index) {
                    // Any element previous to index is given the 'past' class
                    element.classList.add(reverse ? 'future' : 'past');
                }
                else if (i > index) {
                    // Any element subsequent to index is given the 'future' class
                    element.classList.add(reverse ? 'past' : 'future');
                }

                // If this element contains vertical slides
                if (element.querySelector('section')) {
                    element.classList.add('stack');
                }
            }

            // Mark the current slide as present
            slides[index].classList.add('present');
            slides[index].removeAttribute('hidden');

            // If this slide has a state associated with it, add it
            // onto the current state of the deck
            var slideState = slides[index].getAttribute('data-state');
            if (slideState) {
                state = state.concat(slideState.split(' '));
            }

            // If this slide has a data-autoslide attribtue associated use this as
            // autoSlide value otherwise use the global configured time
            var slideAutoSlide = slides[index].getAttribute('data-autoslide');
            if (slideAutoSlide) {
                autoSlide = parseInt(slideAutoSlide, 10);
            }
            else {
                autoSlide = config.autoSlide;
            }

        }
        else {
            // Since there are no slides we can't be anywhere beyond the
            // zeroth index
            index = 0;
        }

        return index;

    }

    /**
     * Updates the progress bar to reflect the current slide.
     */
    function updateProgress() {

        // Update progress if enabled
        if (config.progress && dom.progress) {

            var horizontalSlides = toArray(document.querySelectorAll(HORIZONTAL_SLIDES_SELECTOR));

            // The number of past and total slides
            var totalCount = document.querySelectorAll(SLIDES_SELECTOR + ':not(.stack)').length;
            var pastCount = 0;

            // Step through all slides and count the past ones
            mainLoop: for (var i = 0; i < horizontalSlides.length; i++) {

                var horizontalSlide = horizontalSlides[i];
                var verticalSlides = toArray(horizontalSlide.querySelectorAll('section'));

                for (var j = 0; j < verticalSlides.length; j++) {

                    // Stop as soon as we arrive at the present
                    if (verticalSlides[j].classList.contains('present')) {
                        break mainLoop;
                    }

                    pastCount++;

                }

                // Stop as soon as we arrive at the present
                if (horizontalSlide.classList.contains('present')) {
                    break;
                }

                // Don't count the wrapping section for vertical slides
                if (horizontalSlide.classList.contains('stack') === false) {
                    pastCount++;
                }

            }

            dom.progressbar.style.width = ( pastCount / ( totalCount - 1 ) ) * window.innerWidth + 'px';

        }

    }

    /**
     * Updates the state of all control/navigation arrows.
     */
    function updateControls() {

        if (config.controls && dom.controls) {

            var routes = availableRoutes();
            var fragments = availableFragments();

            // Remove the 'enabled' class from all directions
            dom.controlsLeft.concat(dom.controlsRight)
                .concat(dom.controlsUp)
                .concat(dom.controlsDown)
                .concat(dom.controlsPrev)
                .concat(dom.controlsNext).forEach(function (node) {
                node.classList.remove('enabled');
                node.classList.remove('fragmented');
            });

            // Add the 'enabled' class to the available routes
            if (routes.left) dom.controlsLeft.forEach(function (el) {
                el.classList.add('enabled');
            });
            if (routes.right) dom.controlsRight.forEach(function (el) {
                el.classList.add('enabled');
            });
            if (routes.up) dom.controlsUp.forEach(function (el) {
                el.classList.add('enabled');
            });
            if (routes.down) dom.controlsDown.forEach(function (el) {
                el.classList.add('enabled');
            });

            // Prev/next buttons
            if (routes.left || routes.up) dom.controlsPrev.forEach(function (el) {
                el.classList.add('enabled');
            });
            if (routes.right || routes.down) dom.controlsNext.forEach(function (el) {
                el.classList.add('enabled');
            });

            // Highlight fragment directions
            if (currentSlide) {

                // Always apply fragment decorator to prev/next buttons
                if (fragments.prev) dom.controlsPrev.forEach(function (el) {
                    el.classList.add('fragmented', 'enabled');
                });
                if (fragments.next) dom.controlsNext.forEach(function (el) {
                    el.classList.add('fragmented', 'enabled');
                });

                // Apply fragment decorators to directional buttons based on
                // what slide axis they are in
                if (isVerticalSlide(currentSlide)) {
                    if (fragments.prev) dom.controlsUp.forEach(function (el) {
                        el.classList.add('fragmented', 'enabled');
                    });
                    if (fragments.next) dom.controlsDown.forEach(function (el) {
                        el.classList.add('fragmented', 'enabled');
                    });
                }
                else {
                    if (fragments.prev) dom.controlsLeft.forEach(function (el) {
                        el.classList.add('fragmented', 'enabled');
                    });
                    if (fragments.next) dom.controlsRight.forEach(function (el) {
                        el.classList.add('fragmented', 'enabled');
                    });
                }
            }

        }

    }

    /**
     * Updates the background elements to reflect the current
     * slide.
     */
    function updateBackground() {

        // Update the classes of all backgrounds to match the
        // states of their slides (past/present/future)
        toArray(dom.background.childNodes).forEach(function (backgroundh, h) {

            // Reverse past/future classes when in RTL mode
            var horizontalPast = config.rtl ? 'future' : 'past',
                horizontalFuture = config.rtl ? 'past' : 'future';

            backgroundh.className = 'slide-background ' + ( h < indexh ? horizontalPast : h > indexh ? horizontalFuture : 'present' );

            toArray(backgroundh.childNodes).forEach(function (backgroundv, v) {

                backgroundv.className = 'slide-background ' + ( v < indexv ? 'past' : v > indexv ? 'future' : 'present' );

            });

        });

        // Allow the first background to apply without transition
        setTimeout(function () {
            dom.background.classList.remove('no-transition');
        }, 1);

    }

    /**
     * Determine what available routes there are for navigation.
     *
     * @return {Object} containing four booleans: left/right/up/down
     */
    function availableRoutes() {

        var horizontalSlides = document.querySelectorAll(HORIZONTAL_SLIDES_SELECTOR),
            verticalSlides = document.querySelectorAll(VERTICAL_SLIDES_SELECTOR);

        var routes = {
            left: indexh > 0 || config.loop,
            right: indexh < horizontalSlides.length - 1 || config.loop,
            up: indexv > 0,
            down: indexv < verticalSlides.length - 1
        };

        // reverse horizontal controls for rtl
        if (config.rtl) {
            var left = routes.left;
            routes.left = routes.right;
            routes.right = left;
        }

        return routes;

    }

    /**
     * Returns an object describing the available fragment
     * directions.
     *
     * @return {Object} two boolean properties: prev/next
     */
    function availableFragments() {

        if (currentSlide && config.fragments) {
            var fragments = currentSlide.querySelectorAll('.fragment');
            var hiddenFragments = currentSlide.querySelectorAll('.fragment:not(.visible)');

            return {
                prev: fragments.length - hiddenFragments.length > 0,
                next: !!hiddenFragments.length
            };
        }
        else {
            return {prev: false, next: false};
        }

    }

    /**
     * Start playback of any embedded content inside of
     * the targeted slide.
     */
    function startEmbeddedContent(slide) {

        if (slide) {
            // HTML5 media elements
            toArray(slide.querySelectorAll('video, audio')).forEach(function (el) {
                if (el.hasAttribute('data-autoplay')) {
                    el.play();
                }
            });

            // YouTube embeds
            toArray(slide.querySelectorAll('iframe[src*="youtube.com/embed/"]')).forEach(function (el) {
                if (el.hasAttribute('data-autoplay')) {
                    el.contentWindow.postMessage('{"event":"command","func":"playVideo","args":""}', '*');
                }
            });
        }

    }

    /**
     * Stop playback of any embedded content inside of
     * the targeted slide.
     */
    function stopEmbeddedContent(slide) {

        if (slide) {
            // HTML5 media elements
            toArray(slide.querySelectorAll('video, audio')).forEach(function (el) {
                if (!el.hasAttribute('data-ignore')) {
                    el.pause();
                }
            });

            // YouTube embeds
            toArray(slide.querySelectorAll('iframe[src*="youtube.com/embed/"]')).forEach(function (el) {
                if (!el.hasAttribute('data-ignore') && typeof el.contentWindow.postMessage === 'function') {
                    el.contentWindow.postMessage('{"event":"command","func":"pauseVideo","args":""}', '*');
                }
            });
        }

    }

    /**
     * Reads the current URL (hash) and navigates accordingly.
     */
    function readURL() {

        var hash = window.location.hash;

        // Attempt to parse the hash as either an index or name
        var bits = hash.slice(2).split('/'),
            name = hash.replace(/#|\//gi, '');

        // If the first bit is invalid and there is a name we can
        // assume that this is a named link
        if (isNaN(parseInt(bits[0], 10)) && name.length) {
            // Find the slide with the specified name
            var element = document.querySelector('#' + name);

            if (element) {
                // Find the position of the named slide and navigate to it
                var indices = Reveal.getIndices(element);
                slide(indices.h, indices.v);
            }
            // If the slide doesn't exist, navigate to the current slide
            else {
                slide(indexh, indexv);
            }
        }
        else {
            // Read the index components of the hash
            var h = parseInt(bits[0], 10) || 0,
                v = parseInt(bits[1], 10) || 0;

            slide(h, v);
        }

    }

    /**
     * Updates the page URL (hash) to reflect the current
     * state.
     *
     * @param {Number} delay The time in ms to wait before
     * writing the hash
     */
    function writeURL(delay) {

        if (config.history) {

            // Make sure there's never more than one timeout running
            clearTimeout(writeURLTimeout);

            // If a delay is specified, timeout this call
            if (typeof delay === 'number') {
                writeURLTimeout = setTimeout(writeURL, delay);
            }
            else {
                var url = '/';

                // If the current slide has an ID, use that as a named link
                if (currentSlide && typeof currentSlide.getAttribute('id') === 'string') {
                    url = '/' + currentSlide.getAttribute('id');
                }
                // Otherwise use the /h/v index
                else {
                    if (indexh > 0 || indexv > 0) url += indexh;
                    if (indexv > 0) url += '/' + indexv;
                }

                window.location.hash = url;
            }
        }

    }

    /**
     * Retrieves the h/v location of the current, or specified,
     * slide.
     *
     * @param {HTMLElement} slide If specified, the returned
     * index will be for this slide rather than the currently
     * active one
     *
     * @return {Object} { h: <int>, v: <int>, f: <int> }
     */
    function getIndices(slide) {

        // By default, return the current indices
        var h = indexh,
            v = indexv,
            f;

        // If a slide is specified, return the indices of that slide
        if (slide) {
            var isVertical = isVerticalSlide(slide);
            var slideh = isVertical ? slide.parentNode : slide;

            // Select all horizontal slides
            var horizontalSlides = toArray(document.querySelectorAll(HORIZONTAL_SLIDES_SELECTOR));

            // Now that we know which the horizontal slide is, get its index
            h = Math.max(horizontalSlides.indexOf(slideh), 0);

            // If this is a vertical slide, grab the vertical index
            if (isVertical) {
                v = Math.max(toArray(slide.parentNode.querySelectorAll('section')).indexOf(slide), 0);
            }
        }

        if (!slide && currentSlide) {
            var visibleFragments = currentSlide.querySelectorAll('.fragment.visible');
            if (visibleFragments.length) {
                f = visibleFragments.length;
            }
        }

        return {h: h, v: v, f: f};

    }

    /**
     * Navigate to the next slide fragment.
     *
     * @return {Boolean} true if there was a next fragment,
     * false otherwise
     */
    function nextFragment() {

        if (currentSlide && config.fragments) {
            var fragments = sortFragments(currentSlide.querySelectorAll('.fragment:not(.visible)'));

            if (fragments.length) {
                // Find the index of the next fragment
                var index = fragments[0].getAttribute('data-fragment-index');

                // Find all fragments with the same index
                fragments = currentSlide.querySelectorAll('.fragment[data-fragment-index="' + index + '"]');

                toArray(fragments).forEach(function (element) {
                    element.classList.add('visible');

                    // Notify subscribers of the change
                    dispatchEvent('fragmentshown', {fragment: element});
                });

                updateControls();
                return true;
            }
        }

        return false;

    }

    /**
     * Navigate to the previous slide fragment.
     *
     * @return {Boolean} true if there was a previous fragment,
     * false otherwise
     */
    function previousFragment() {

        if (currentSlide && config.fragments) {
            var fragments = sortFragments(currentSlide.querySelectorAll('.fragment.visible'));

            if (fragments.length) {
                // Find the index of the previous fragment
                var index = fragments[fragments.length - 1].getAttribute('data-fragment-index');

                // Find all fragments with the same index
                fragments = currentSlide.querySelectorAll('.fragment[data-fragment-index="' + index + '"]');

                toArray(fragments).forEach(function (f) {
                    f.classList.remove('visible');

                    // Notify subscribers of the change
                    dispatchEvent('fragmenthidden', {fragment: f});
                });

                updateControls();
                return true;
            }
        }

        return false;

    }

    /**
     * Cues a new automated slide if enabled in the config.
     */
    function cueAutoSlide() {

        clearTimeout(autoSlideTimeout);

        // Cue the next auto-slide if enabled
        if (autoSlide && !isPaused() && !isOverview()) {
            autoSlideTimeout = setTimeout(navigateNext, autoSlide);
        }

    }

    /**
     * Cancels any ongoing request to auto-slide.
     */
    function cancelAutoSlide() {

        clearTimeout(autoSlideTimeout);

    }

    function navigateLeft() {

        // Reverse for RTL
        if (config.rtl) {
            if (( isOverview() || nextFragment() === false ) && availableRoutes().left) {
                slide(indexh + 1);
            }
        }
        // Normal navigation
        else if (( isOverview() || previousFragment() === false ) && availableRoutes().left) {
            slide(indexh - 1);
        }

    }

    function navigateRight() {

        // Reverse for RTL
        if (config.rtl) {
            if (( isOverview() || previousFragment() === false ) && availableRoutes().right) {
                slide(indexh - 1);
            }
        }
        // Normal navigation
        else if (( isOverview() || nextFragment() === false ) && availableRoutes().right) {
            slide(indexh + 1);
        }

    }

    function navigateUp() {

        // Prioritize hiding fragments
        if (( isOverview() || previousFragment() === false ) && availableRoutes().up) {
            slide(indexh, indexv - 1);
        }

    }

    function navigateDown() {

        // Prioritize revealing fragments
        if (( isOverview() || nextFragment() === false ) && availableRoutes().down) {
            slide(indexh, indexv + 1);
        }

    }

    /**
     * Navigates backwards, prioritized in the following order:
     * 1) Previous fragment
     * 2) Previous vertical slide
     * 3) Previous horizontal slide
     */
    function navigatePrev() {

        // Prioritize revealing fragments
        if (previousFragment() === false) {
            if (availableRoutes().up) {
                navigateUp();
            }
            else {
                // Fetch the previous horizontal slide, if there is one
                var previousSlide = document.querySelector(HORIZONTAL_SLIDES_SELECTOR + '.past:nth-child(' + indexh + ')');

                if (previousSlide) {
                    var v = ( previousSlide.querySelectorAll('section').length - 1 ) || undefined;
                    var h = indexh - 1;
                    slide(h, v);
                }
            }
        }

    }

    /**
     * Same as #navigatePrev() but navigates forwards.
     */
    function navigateNext() {

        // Prioritize revealing fragments
        if (nextFragment() === false) {
            availableRoutes().down ? navigateDown() : navigateRight();
        }

        // If auto-sliding is enabled we need to cue up
        // another timeout
        cueAutoSlide();

    }


    // --------------------------------------------------------------------//
    // ----------------------------- EVENTS -------------------------------//
    // --------------------------------------------------------------------//


    /**
     * Handler for the document level 'keydown' event.
     *
     * @param {Object} event
     */
    function onDocumentKeyDown(event) {

        // Check if there's a focused element that could be using
        // the keyboard
        var activeElement = document.activeElement;
        var hasFocus = !!( document.activeElement && ( document.activeElement.type || document.activeElement.href || document.activeElement.contentEditable !== 'inherit' ) );

        // Disregard the event if there's a focused element or a
        // keyboard modifier key is present
        if (hasFocus || (event.shiftKey && event.keyCode !== 32) || event.altKey || event.ctrlKey || event.metaKey) return;

        // While paused only allow "unpausing" keyboard events (b and .)
        if (isPaused() && [66, 190, 191].indexOf(event.keyCode) === -1) {
            return false;
        }

        var triggered = false;

        // 1. User defined key bindings
        if (typeof config.keyboard === 'object') {

            for (var key in config.keyboard) {

                // Check if this binding matches the pressed key
                if (parseInt(key, 10) === event.keyCode) {

                    var value = config.keyboard[key];

                    // Calback function
                    if (typeof value === 'function') {
                        value.apply(null, [event]);
                    }
                    // String shortcuts to reveal.js API
                    else if (typeof value === 'string' && typeof Reveal[value] === 'function') {
                        Reveal[value].call();
                    }

                    triggered = true;

                }

            }

        }

        // 2. System defined key bindings
        if (triggered === false) {

            // Assume true and try to prove false
            triggered = true;

            switch (event.keyCode) {
                // p, page up
                case 80:
                case 33:
                    navigatePrev();
                    break;
                // n, page down
                case 78:
                case 34:
                    navigateNext();
                    break;
                // h, left
                case 72:
                case 37:
                    navigateLeft();
                    break;
                // l, right
                case 76:
                case 39:
                    navigateRight();
                    break;
                // k, up
                case 75:
                case 38:
                    navigateUp();
                    break;
                // j, down
                case 74:
                case 40:
                    navigateDown();
                    break;
                // home
                case 36:
                    slide(0);
                    break;
                // end
                case 35:
                    slide(Number.MAX_VALUE);
                    break;
                // space
                case 32:
                    isOverview() ? deactivateOverview() : event.shiftKey ? navigatePrev() : navigateNext();
                    break;
                // return
                case 13:
                    isOverview() ? deactivateOverview() : triggered = false;
                    break;
                // b, period, Logitech presenter tools "black screen" button
                case 66:
                case 190:
                case 191:
                    togglePause();
                    break;
                // f
                case 70:
                    enterFullscreen();
                    break;
                default:
                    triggered = false;
            }

        }

        // If the input resulted in a triggered action we should prevent
        // the browsers default behavior
        if (triggered) {
            event.preventDefault();
        }
        else if (event.keyCode === 27 && supports3DTransforms) {
            toggleOverview();

            event.preventDefault();
        }

        // If auto-sliding is enabled we need to cue up
        // another timeout
        cueAutoSlide();

    }

    /**
     * Handler for the 'touchstart' event, enables support for
     * swipe and pinch gestures.
     */
    function onTouchStart(event) {

        touch.startX = event.touches[0].clientX;
        touch.startY = event.touches[0].clientY;
        touch.startCount = event.touches.length;

        // If there's two touches we need to memorize the distance
        // between those two points to detect pinching
        if (event.touches.length === 2 && config.overview) {
            touch.startSpan = distanceBetween({
                x: event.touches[1].clientX,
                y: event.touches[1].clientY
            }, {
                x: touch.startX,
                y: touch.startY
            });
        }

    }

    /**
     * Handler for the 'touchmove' event.
     */
    function onTouchMove(event) {

        // Each touch should only trigger one action
        if (!touch.handled) {
            var currentX = event.touches[0].clientX;
            var currentY = event.touches[0].clientY;

            // If the touch started off with two points and still has
            // two active touches; test for the pinch gesture
            if (event.touches.length === 2 && touch.startCount === 2 && config.overview) {

                // The current distance in pixels between the two touch points
                var currentSpan = distanceBetween({
                    x: event.touches[1].clientX,
                    y: event.touches[1].clientY
                }, {
                    x: touch.startX,
                    y: touch.startY
                });

                // If the span is larger than the desire amount we've got
                // ourselves a pinch
                if (Math.abs(touch.startSpan - currentSpan) > touch.threshold) {
                    touch.handled = true;

                    if (currentSpan < touch.startSpan) {
                        activateOverview();
                    }
                    else {
                        deactivateOverview();
                    }
                }

                event.preventDefault();

            }
            // There was only one touch point, look for a swipe
            else if (event.touches.length === 1 && touch.startCount !== 2) {

                var deltaX = currentX - touch.startX,
                    deltaY = currentY - touch.startY;

                if (deltaX > touch.threshold && Math.abs(deltaX) > Math.abs(deltaY)) {
                    touch.handled = true;
                    navigateLeft();
                }
                else if (deltaX < -touch.threshold && Math.abs(deltaX) > Math.abs(deltaY)) {
                    touch.handled = true;
                    navigateRight();
                }
                else if (deltaY > touch.threshold) {
                    touch.handled = true;
                    navigateUp();
                }
                else if (deltaY < -touch.threshold) {
                    touch.handled = true;
                    navigateDown();
                }

                event.preventDefault();

            }
        }
        // There's a bug with swiping on some Android devices unless
        // the default action is always prevented
        else if (navigator.userAgent.match(/android/gi)) {
            event.preventDefault();
        }

    }

    /**
     * Handler for the 'touchend' event.
     */
    function onTouchEnd(event) {

        touch.handled = false;

    }

    /**
     * Convert pointer down to touch start.
     */
    function onPointerDown(event) {

        if (event.pointerType === event.MSPOINTER_TYPE_TOUCH) {
            event.touches = [{clientX: event.clientX, clientY: event.clientY}];
            onTouchStart(event);
        }

    }

    /**
     * Convert pointer move to touch move.
     */
    function onPointerMove(event) {

        if (event.pointerType === event.MSPOINTER_TYPE_TOUCH) {
            event.touches = [{clientX: event.clientX, clientY: event.clientY}];
            onTouchMove(event);
        }

    }

    /**
     * Convert pointer up to touch end.
     */
    function onPointerUp(event) {

        if (event.pointerType === event.MSPOINTER_TYPE_TOUCH) {
            event.touches = [{clientX: event.clientX, clientY: event.clientY}];
            onTouchEnd(event);
        }

    }

    /**
     * Handles mouse wheel scrolling, throttled to avoid skipping
     * multiple slides.
     */
    function onDocumentMouseScroll(event) {

        if (Date.now() - lastMouseWheelStep > 600) {

            lastMouseWheelStep = Date.now();

            var delta = event.detail || -event.wheelDelta;
            if (delta > 0) {
                navigateNext();
            }
            else {
                navigatePrev();
            }

        }

    }

    /**
     * Clicking on the progress bar results in a navigation to the
     * closest approximate horizontal slide using this equation:
     *
     * ( clickX / presentationWidth ) * numberOfSlides
     */
    function onProgressClicked(event) {

        event.preventDefault();

        var slidesTotal = toArray(document.querySelectorAll(HORIZONTAL_SLIDES_SELECTOR)).length;
        var slideIndex = Math.floor(( event.clientX / dom.wrapper.offsetWidth ) * slidesTotal);

        slide(slideIndex);

    }

    /**
     * Event handler for navigation control buttons.
     */
    function onNavigateLeftClicked(event) {
        event.preventDefault();
        navigateLeft();
    }

    function onNavigateRightClicked(event) {
        event.preventDefault();
        navigateRight();
    }

    function onNavigateUpClicked(event) {
        event.preventDefault();
        navigateUp();
    }

    function onNavigateDownClicked(event) {
        event.preventDefault();
        navigateDown();
    }

    function onNavigatePrevClicked(event) {
        event.preventDefault();
        navigatePrev();
    }

    function onNavigateNextClicked(event) {
        event.preventDefault();
        navigateNext();
    }

    /**
     * Handler for the window level 'hashchange' event.
     */
    function onWindowHashChange(event) {

        readURL();

    }

    /**
     * Handler for the window level 'resize' event.
     */
    function onWindowResize(event) {

        layout();

    }

    /**
     * Invoked when a slide is and we're in the overview.
     */
    function onOverviewSlideClicked(event) {

        // TODO There's a bug here where the event listeners are not
        // removed after deactivating the overview.
        if (eventsAreBound && isOverview()) {
            event.preventDefault();

            var element = event.target;

            while (element && !element.nodeName.match(/section/gi)) {
                element = element.parentNode;
            }

            if (element && !element.classList.contains('disabled')) {

                deactivateOverview();

                if (element.nodeName.match(/section/gi)) {
                    var h = parseInt(element.getAttribute('data-index-h'), 10),
                        v = parseInt(element.getAttribute('data-index-v'), 10);

                    slide(h, v);
                }

            }
        }

    }

    /**
     * Handles clicks on links that are set to preview in the
     * iframe overlay.
     */
    function onPreviewLinkClicked(event) {

        var url = event.target.getAttribute('href');
        if (url) {
            openPreview(url);
            event.preventDefault();
        }

    }


    // --------------------------------------------------------------------//
    // ------------------------------- API --------------------------------//
    // --------------------------------------------------------------------//


    return {
        initialize: initialize,
        configure: configure,
        sync: sync,

        // Navigation methods
        slide: slide,
        left: navigateLeft,
        right: navigateRight,
        up: navigateUp,
        down: navigateDown,
        prev: navigatePrev,
        next: navigateNext,
        prevFragment: previousFragment,
        nextFragment: nextFragment,

        // Deprecated aliases
        navigateTo: slide,
        navigateLeft: navigateLeft,
        navigateRight: navigateRight,
        navigateUp: navigateUp,
        navigateDown: navigateDown,
        navigatePrev: navigatePrev,
        navigateNext: navigateNext,

        // Forces an update in slide layout
        layout: layout,

        // Returns an object with the available routes as booleans (left/right/top/bottom)
        availableRoutes: availableRoutes,

        // Returns an object with the available fragments as booleans (prev/next)
        availableFragments: availableFragments,

        // Toggles the overview mode on/off
        toggleOverview: toggleOverview,

        // Toggles the "black screen" mode on/off
        togglePause: togglePause,

        // State checks
        isOverview: isOverview,
        isPaused: isPaused,

        // Adds or removes all internal event listeners (such as keyboard)
        addEventListeners: addEventListeners,
        removeEventListeners: removeEventListeners,

        // Returns the indices of the current, or specified, slide
        getIndices: getIndices,

        // Returns the slide at the specified index, y is optional
        getSlide: function (x, y) {
            var horizontalSlide = document.querySelectorAll(HORIZONTAL_SLIDES_SELECTOR)[x];
            var verticalSlides = horizontalSlide && horizontalSlide.querySelectorAll('section');

            if (typeof y !== 'undefined') {
                return verticalSlides ? verticalSlides[y] : undefined;
            }

            return horizontalSlide;
        },

        // Returns the previous slide element, may be null
        getPreviousSlide: function () {
            return previousSlide;
        },

        // Returns the current slide element
        getCurrentSlide: function () {
            return currentSlide;
        },

        // Returns the current scale of the presentation content
        getScale: function () {
            return scale;
        },

        // Returns the current configuration object
        getConfig: function () {
            return config;
        },

        // Helper method, retrieves query string as a key/value hash
        getQueryHash: function () {
            var query = {};

            location.search.replace(/[A-Z0-9]+?=(\w*)/gi, function (a) {
                query[a.split('=').shift()] = a.split('=').pop();
            });

            return query;
        },

        // Returns true if we're currently on the first slide
        isFirstSlide: function () {
            return document.querySelector(SLIDES_SELECTOR + '.past') == null ? true : false;
        },

        // Returns true if we're currently on the last slide
        isLastSlide: function () {
            if (currentSlide && currentSlide.classList.contains('.stack')) {
                return currentSlide.querySelector(SLIDES_SELECTOR + '.future') == null ? true : false;
            }
            else {
                return document.querySelector(SLIDES_SELECTOR + '.future') == null ? true : false;
            }
        },

        // Forward event binding to the reveal DOM element
        addEventListener: function (type, listener, useCapture) {
            if ('addEventListener' in window) {
                ( dom.wrapper || document.querySelector('.reveal') ).addEventListener(type, listener, useCapture);
            }
        },
        removeEventListener: function (type, listener, useCapture) {
            if ('addEventListener' in window) {
                ( dom.wrapper || document.querySelector('.reveal') ).removeEventListener(type, listener, useCapture);
            }
        }
    };

})();
